Cover 'repl' package with tests

Pretty self-descriptive issue 😃  We want to cover the repository source code with tests as much as we can. This Particular issue scopes to [repl package](https://github.com/Neurostep/go-nate/blob/fa4e27ed12b3d90a8495271c7b71c642ad679e35/internal/repl/repl.go#L1)